1. Field of the Invention
The present invention relates to a hafnium-containing material for film formation as a source suitable for producing a hafnium-containing thin film useful as paraelectric thin film, optical thin film, catalyst thin film, solid electrolyte thin film and the like and a method for producing the same, and to a process for producing the hafnium-containing thin film made of the material produced by the above method. More specifically, the present invention provides a material useful for forming a hafnium-containing thin film such as Si—O—Hf thin film, HfO2 thin film, etc., preferable as a source for producing a hafnium-containing thin film by metal organic chemical vapor deposition process (hereinafter, abbreviated as “MOCVD process”), a method for producing the same, and a process for production of a hafnium-containing thin film using the produced film forming material.
2. Description of the Related Art
Silicon oxide film has been widely known and has been commonly used as high-dielectric gate insulation film. Recently, film thickness of the silicon oxide film tends to be thinner as semiconductor devices become more highly integrated. If a silicon oxide (hereinafter, abbreviated as “SiO2”) film having the thickness of 100 nm or less is used, reduced insulation effect due to tunnel current flowing across the thin film typically occurs, which poses a limitation in obtaining films thinner than such thickness to suitably function as the insulation film.
In view of the above, a novel gate insulation film is required in replacing of SiO2 film such as a hafnium-containing thin film, more particularly, HfO2 or HfO2—SiO2 as a substitute for SiO2 film. One of conventional methods for producing such thin films, MOD process such as sputtering, ion-plating or applied-pyrolysis, sol-gel method has been known. However, as a result of considering a variety of characteristics such as composition control, step coverage, conformity with processes for production of semiconductor device, etc., MOCVD process is being considered lately as an ideal film formation method.
Moreover, hafnium tert-butoxide (hereinafter, referred to as Hf(OtBu)4) or hafnium tetrakis dipivaloylmethanate (hereinafter, referred to as Hf(DPM)4) having coordinate covalent bonds with 2,2,6,6-tetramethyl-3,5-heptanedione residue (hereinafter, referred to as DPM) is attracting attention as the material for forming hafnium-containing thin film. However, Hf(OtBu)4) shows poor reproducibility when the thin film is formed at low temperature while Hf(DPM)4 has a disadvantage of forming film at high temperature in spite of good stability.
In order to solve the problems mentioned above, Hf(DPM)4 obtained by adding Hafnium and purified dipivaloylmethane in an organic solvent purified and dehydrated under inert gas atmosphere, directly reacting the obtained solution together with reflux and heating followed by cooling the reacted product to be extracted, and by sufficiently purifying the resultant crude crystalline product by means of recrystallization is disclosed(for example, see Japanese Unexamined Patent Application Publication No. 2002-249455 (Patent Document 1)). As a result of purification by the above process, obtained is high-purity Hf complex containing 0.01 wt.ppm or less of metal impurities and with a purity of 99.99999% by weight or more.
Further, it has been disclosed a process for forming Hafnium-containing thin film using MOCVD process, which comprises steps of introducing at least one or multiple organic source material(s) represented by M[N(C2H5)2]4 wherein M is a metallic element, typically containing Si; depositing metallic film or metal compound film using CVD process; and conducting heat treatment for the deposited product at a desired temperature higher than the deposition temperature after the deposition step (for example, see Japanese Unexamined Patent Application Publication No. 2002-167672 (Patent Document 2)). By this process, film side of a semiconductor device and/or electronic device is deposited with metal component and compound thereof with excellent control and uniformity even when there is unevenness on the film side, thereby making it possible to achieve production of the semiconductor device and/or electronic device having improved characteristics.
However, Patent Document 1 still has a disadvantage of forming film in high temperature owing to a source material, that is, although Hf(DPM)4 provides hafnium-containing thin film with excellent property by using a source material of high-purity, adverse effects are imparted to a substrate caused by the heating process.
Furthermore, the conventional technologies illustrated above have a problem in that the compounds such as Hf(OtBu)4, Hf(DPM)4 described in Japanese Unexamined Patent Application Publication No. 2002-249455 or M[N(C2H5)2]4 described in Japanese Unexamined Patent Application Publication No. 2002-167672 did not initially include zirconium element (Zr), but contained Zr as one of impurities during the synthetic reaction. This is because Zr has specific chemical structure and/or behavior substantially identical to Hf, making it difficult from being easily removed. If Zr as the inevitable impurity is contained in the material for forming hafnium-containing film, it causes the material to have poor volatility and decreases the film formation rate, or it deteriorates step coverage of the hafnium-containing thin film.